Although the prior art teaches a number of sonar or ultrasonic ranging devices, typical of which is that shown in U.S. Pat. No. 3,360,775 to Schroeder, and U.S. Pat. No. 3,922,629 to Hayakawa, there do not appear to be any prior art ultrasonic ranging devices specifically adapted for use by most drivers of passenger vehicles.
Although an ultrasonic ranging device having a single transducer used for both transmission and reception is highly desirable, it may be appreciated that a ranging device having a plurality of transducers, each being able to transmit and receive, is particularly useful for a vehicle, such as an automobile. This is because a single transducer, such as the transducer employed in the apparatus of the parent application, normally covers a limited angular area. If the single transducer is mounted in the bumper of a vehicle, the transducer may not sense objects which are positioned relatively close to the bumper of the car, but which are outside the limited angular area. It is desirable, therefore, to use a plurality of transducers.
It is also necessary to eliminate cross-talk between adjacent transducers. Cross-talk can result in false return from a first transducer picking up a transmitted signal from a second tranducer. This would cause an incorrect warning indication to be provided to a vehicle operator.
Thus, it is clear that what is needed is a relatively low cost ultrasonic ranging system having a plurality of transducers, each transducer being used for both transmitting and receiving, which can inform the driver through the use of an indicator means that a vehicle is within a predetermined range of an obstacle.